Liquid crystal macrocycles

ABSTRACT

A material of general formula I: ##STR1## where E=0 indicates a non-cyclic system, and E=1 indicates a cyclic system; 
     G is R 3  SiR 1  R 2  (O) k   
     R 1 , R 2 , R 3  are independently selected from C 1-16  alkyl which may be partly or fully halogenated, H and formula IA: ##STR2##  wherein Y is a propylene group which may be partially halogenated with fluorine or chlorine and Y 1  is independently selected from COO, OCO, O, S, CHOH, CHF, CO or CH 2  ; 
     Q and Q 1  are independently selected from (CH 2 ) n  wherein one or more non-adjacent methylenes may be replaced by O and 
     n=0-20; 
     Z and Z 1  are independently selected from O, S, single covalent bond, COO or OCO; ##STR3## represents a mesogenic group and is given by the general structure II ##STR4##  A, B, D are selected from the following rings: ##STR5## the above rings may be substituted with one or more of the following substituents in at least one of the available substitution positions: F, Cl, Br, CH 3 , CN, OR, R or NCS where R is a C 1-5  branched or straight chain alkyl provided that the total number of rings present is not greater than 4; and W 1  and W 2  are independently COO, OCO, single bond, CH 2  CH 2 , CH 2  O, OCH 2 , O, S, CH═CH, C.tbd.C, or N═N.

This invention concerns liquid crystal macrocycles, and their use inliquid crystal mixtures and devices.

BACKGROUND OF THE INVENTION

Liquid crystals can exist in various phases. In essence there are threedifferent classes of liquid crystalline material, each possessing acharacteristic molecular arrangement. These classes are nematic, chiralnematic (cholesteric) and smectic. A wide range of smectic phasesexists, for example smectic A and smectic C. Some liquid crystalmaterials possess a number of liquid crystal phases on varying thetemperature, others have just one phase. For example, a liquid crystalmaterial may show the following phases on being cooled from theisotropic phase:- isotropic - nematic - smectic A - smectic C - solid.If a material is described as being smectic A then it means that thematerial possesses a smectic A phase over a useful working temperaturerange.

Materials possessing a smectic A (S_(A)) phase may exhibit anelectroclinic effect. The electroclinic effect was first described by SGaroff and R Meyer, Phys. Rev. Lett., 38, 848 (1977). An electroclinicdevice has also been described in UK patent application GB-2 244 566 A.This particular device helps to overcome the poor alignment problems ofelectroclinic (EC) devices using a surface alignment that gives asurface tilt within a small range of angles.

When a smectic A phase is composed of chiral molecules, it may exhibitan electroclinic effect, i.e. a direct coupling of molecular tilt toapplied field. The origin of the electroclinic effect in a smectic Aphase composed of chiral polar molecules has been described by Garoffand Meyer as follows. The application of an electric field parallel tothe smectic layers of such a smectic A phase biases the free rotation ofthe transverse molecular dipoles and therefore produces a non-zeroaverage of the transverse component of the molecular polarisation. Whensuch a dipole moment is present and coupled to the molecular chirality,a tilt of the long molecular axis (the director) is induced in a planeperpendicular to the dipole moment.

In thin samples, for example 1-3 μm, and with the smectic layers tiltedor perpendicular with respect to the glass plates the electrocliniceffect is detectable at low applied fields.

In an aligned smectic A sample a tilt of the director is directlyrelated to a tilt of the optic axis. The electroclinic effect results ina linear electro-optic response. The electro-optic effect can manifestitself as a modulation of the effective birefringence of the device.

Electroclinic (EC) devices are useful, for example, in spatial lightmodulators having an output that varies linearly with applied voltage. Afurther advantage of EC devices is that they have high speed responsetimes, much faster than twisted nematic type devices. One known type offerroelectric device is bistable, in contrast the EC device is notbistable and has an output that varies linearly with applied voltage.

The electroclinic effect is sometimes referred to as the soft-modeeffect see G Andersson et al in Appl. Phys. Lett., 51, 9, (1987).

In general terms, regarding the electroclinic effect, it is advantageousif on applying a small voltage there results a large induced tilt. Anincrease in induced tilt may result in an increase in contrast ratio. Itis also advantageous if a large induced tilt can be obtained at as low avoltage as possible.

It is also advantageous if the relationship between molecular inducedtilt and applied voltage is temperature independent. When an increase inapplied voltage results in little or no change in induced tilt then thematerial being tested is generally referred to as exhibiting asaturation voltage effect.

BY S_(A) * is meant a S_(A) phase which contains some proportion ofchirat molecules.

Cholesteric or chiral nematic liquid crystals possess a twisted helicalstructure which is capable of responding to a temperature change througha change in the helical pitch length. Therefore as the temperature ischanged, then the wavelength of the light reflected from the planarcholesteric structure will change and if the reflected light covers thevisible range then distinct changes in colour occur as the temperaturevaries. This means that there are many possible applications includingthe areas of thermography and thermooptics.

The cholesteric mesophase differs from the nematic phase in that in thecholesteric phase the director is not constant in space but undergoes ahelical distortion. The pitch length for the helix is a measure of thedistance for the director to turn through 360°.

By definition, a cholesteric material is chiral material. Cholestericmaterials may also be used in electro-optical displays as dopants, forexample in twisted nematic displays where they may be used to removereverse twist defects. They may also be used in cholesteric to nematicdyed phase change displays where they may be used to enhance contrast bypreventing wave-guiding.

Thermochromic applications of cholesteric liquid crystal materialsusually use thin film preparations of the materials which are thenviewed against a black background. These temperature sensing devices maybe placed into a number of applications involving thermometry, medicalthermography, non-destructive testing, radiation sensing and fordecorative purposes. Examples of these may be found in D G McDonnell inThermotropic Liquid Crystals, Critical Reports on Applied Chemistry,Vol. 22, edited by G W Gray, 1987 pp 120-44; this reference alsocontains a general description of thermochromic cholesteric liquidcrystals.

Generally, commercial thermochromic applications require the formulationof mixtures which possess low melting points, short pitch lengths andsmectic transitions just below the required temperature-sensing region.Preferably the mixture or material should retain a low melting point andhigh smectic--cholesteric transition temperatures.

In general, thermochromic liquid crystal devices have a thin film ofcholesterogen sandwiched between a transparent supporting substrate anda black absorbing layer. One of the fabrication methods involvesproducing an `ink` with the liquid crystal by encapsulating it in apolymer and using printing technologies to apply it to the supportingsubstrate. Methods of manufacturing the inks include gelatinmicroencapsulation, U.S. Pat. No. 3,585,318 and polymer dispersion, U.S.Pat. Nos. 1,161,039 and 3,872,050. One of the ways for preparingwell-aligned thin-film structures of cholesteric liquid crystalsinvolves laminating the liquid crystal between two embossed plasticsheets. This technique is described in UK patent 2,143,323.

Ferroelectric smectic liquid crystal materials, which can be produced bymixing an achiral host and a chiral dopant, use the ferroelectricproperties of the tilted chiral smectic C, F, G, H, I, J and K phases.The chiral smectic C phase is denoted S_(C) * with the asterisk denotingchirality. The S_(C) phase is generally considered to be the most usefulas it is the least viscous. Ferroelectric smectic liquid crystalmaterials should ideally possess the following characteristics: lowviscosity, controllable spontaneous polarisation (Ps) and an S_(C) phasethat persists over a broad temperature range which should includeambient temperature and exhibits chemical and photochemical stability.Materials which possess these characteristics offer the prospect of veryfast switching liquid crystal containing devices. Some applications offerroelectric liquid crystals are described by J S Patel and J W Goodbyin Opt. Eng., 1987, 26, 273.

In ferroelectric liquid crystal devices the molecules switch betweendifferent alignment directions depending on the polarity of an appliedelectric field. These devices can be arranged to exhibit bistabilitywhere the molecules tend to remain in one of two states until switchedto the other switched state. Such devices are termed surface stabilisedferroelectric devices, e.g. as described in U.S. Pat. No. 5,061,047 andU.S. Pat. No. 4,367,924 and U.S. Pat. No. 4,563,059. This bistabilityallows the multiplex addressing of quite large and complex devices.

One common multiplex display has display elements, i.e. pixels, arrangedin an X, Y matrix format for the display of for example alpha numericcharacters. The matrix format is provided by forming the electrodes onone slide as a series of column electrodes, and the electrodes on theother slide as a series of row electrodes. The intersections betweeneach column and row form addressable elements or pixels. Other matrixlayouts are known, e.g. seven bar numeric displays.

There are many different multiplex addressing schemes. A common featureinvolves the application of a voltage, called a strobe voltage to eachrow or line in sequence. Coincidentally with the strobe applied at eachrow, appropriate voltages, called data voltages, are applied to allcolumn electrodes. The differences between the different schemes lies inthe shape of the strobe and data voltage waveforms.

Other addressing schemes are described in GB-2,146, 473-A;GB-2,173,336-A; GB-2,173, 337-A; GB-2, 173629-A; WO 89/05025; Harada etal 1985 S.I.D. Paper 8.4 pp 131-134; Lagerwall et al 1985 I.D.R.C. pp213-221 and P Maltese et al in Proc 1988 I.D.R.C. pp 90-101 FastAddressing for Ferroelectric LC Display Panels.

The material may be switched between its two states by two strobe pulsesof opposite sign, in conjunction with a data waveform. Alternatively, ablanking pulse may be used to switch the material into one of itsstates. Periodically the sign of the blanking and the strobe pulses maybe alternated to maintain a net d.c. value.

These blanking pulses are normally greater in amplitude and length ofapplication than the strobe pulses so that the material switchesirrespective of which of the two data waveforms is applied to any oneintersection. Blanking pulses may be applied on a line by line basisahead of the strobe, or the whole display may be blanked at one time, ora group of lines may be simultaneously blanked.

It is well known in the field of ferroelectric liquid crystal devicetechnology that in order to achieve the highest performance fromdevices, it is important to use mixtures of compounds which givematerials possessing the most suitable ferroelectric smecticcharacteristics for particular types of devices.

Devices can be assessed for speed by consideration of the response timevs pulse voltage curve. This relationship may show a minimum in theswitching time (t_(min)) at a particular applied voltage (V_(min)). Atvoltages higher or lower than V_(min) the switching time is longer thant_(min). It is well understood that devices having such a minimum intheir response time vs voltage curve can be multiplex driven at highduty ratio with higher contrast than other ferroelectric liquid crystaldevices. It is preferred that the said minimum in the response time vsvoltage curve should occur at low applied voltage and at short pulselength respectively to allow the device to be driven using a low voltagesource and fast frame address refresh rate.

Typical known materials (where materials are a mixture of compoundshaving suitable liquid crystal characteristics) which do not allow sucha minimum when included in a ferroelectric device include thecommercially available materials known as SCE13 and ZLI-3654 (bothsupplied by Merck UK Ltd, Poole, Dorset). A device which does show sucha minimum may be constructed according to PCT GB 88/01004 and utilisingmaterials such as e.g. commercially available SCE8 (Merck UK Ltd). Otherexamples of prior art materials are exemplified by PCT/GB 86/00040, PCTGB 87/00441 and UK 2232416B.

The unit that is the basic building block of a polymer is called amonomer.

The polymerisation process i.e. the formation of a polymer from itsconstituent monomers does not usually create polymers of uniformmolecular weight, rather what is created is a distribution of molecularweights. In order to describe a sample of polymer it is necessary tostate the average number of monomers in a polymer this is called thedegree of polymerisation (D.P). By how much the majority of polymermolecules differ from this average value (or to describe the spread ofmolecular weight) is called the polydispersity.

A number of different average molecular weights can be drawn from gelpermeation chromatography (GPC) for a given sample including: M_(n)--number average molecular weight and M_(w) --weight average molecularweight. The value used to calculate D.P. is usually M_(n) andpolydispersity is usually defined as M_(w) /M_(n).

Polymers can be made from different types of monomers, in which case thepolymer is called a co-polymer. If two types of monomer join in a randomfashion then the polymer is called a random co-polymer. If the twomonomers form short sequences of one type first which then combine toform the final polymer then a block copolymer results. If shortsequences of one of the monomers attach themselves as side chains tolong sequences consisting of the other type of monomer then the polymeris referred to as a graft copolymer.

In liquid crystal (LC) polymers the monomers can be attached together inessentially two ways. The liquid crystal part or mesogenic unit of thepolymer may be part of the polymer backbone resulting in a main chain LCpolymer. Alternatively, the mesogenic unit may be attached to thepolymer backbone as a pendant group i.e. extending away from the polymerbackbone; this results in a side-chain LC polymer. These different typesof polymer liquid crystal are represented schematically below. Themesogenic units are depicted by the rectangles. ##STR6##

The side chain liquid crystal polymer can generally be thought of ascontaining a flexible polymer with rigid segments (the mesogenic unit)attached along its length by short flexible (or rigid) units. It is theanisotropic, rigid section of the mesogenic units that displayorientational order in the liquid crystal phases. In order to affect thephases exhibited by the liquid crystal and the subsequent opticalproperties there are many features which can be altered, some of thesefeatures are particularly pertinent to side-chain liquid crystalpolymers. One of these features is the flexible part that joins themesogenic unit to the polymer backbone which is generally referred to asthe spacer group. The length and flexibility of this spacer group can bealtered.

A number of side-chain liquid crystal polymers are known, for examplesee GB 2146787 A.

Liquid crystal polyacrylates are a known class of liquid crystal polymer(LCP). LCPs are known and used in electro-optic applications, forexample in pyroelectric devices, non-linear optical devices and opticalstorage devices. For example see GB 2146787 and Makromol. Chem. (1985)186 2639-47.

Side-chain liquid crystal polyacrylates are described in PolymerCommunications (1988), 24, 364-365 e.g. of formula: ##STR7## where(CH₂)_(m) is the flexible spacer group and X is the side-chain mesogenicunit and R is hydrogen or alkyl.

Side-chain liquid crystal poiychloroacrylates are described in Makromol.Chem. Rapid Commun. (1984), 5, 393-398 e.g. of formula: ##STR8## where Ris chlorine.

Patent Application PCT GB 94/00662 describes amongst other things theuse of the Baylis-Hillman Reaction to make a range of novel liquidcrystal polymers.

A method for the preparation of polyacrylate homo- or co-polymers havingthe following repeat unit is described in UK patent application GB9203730.8 ##STR9## R₁ and R₂ are independently alkyl or hydrogen, R₃ isalkyl, hydrogen or chlorine, m is O or an integer 1-20, W is a linkagegroup COO or OOC or O and X is a mesogenic group.

One of the main problems with liquid crystal polymers is that they areextremely difficult to align in devices. Essentially there are twotechniques which have been used for aligning liquid crystal polymers. Itis possible to try to align the liquid crystal polymer in a similarmanner as a low molar mass liquid crystal, which is described in moredetail below. Alternatively, mechanical techniques can be used such asshearing. Typically mechanical shearing is performed over hot rollers,this technique is generally only suitable for flexible substrates. It ispossible to shear a sample between glass slides however the glass slidescannot be sealed in the conventional manner.

Materials and Assembling Process of LCDs by Morozumi in Liquid CrystalsApplications and uses, vol. 1 Ed. Bahadur, World Scientific PublishingCo, Pte. Ltd, 1990 pp 171-194 and references therein as the titlesuggests discusses methods for assembling liquid crystal devices.

The technique for aligning low molar mass liquid crystals is typicallyas follows. Transparent electrodes are fabricated on the surfaces of thesubstrates, the substrates typically being made of glass e.g. glassslides. In twisted nematic or super twisted nematic devices, forexample, an alignment process is necessary for both substrates. A thinalignment layer is deposited to align the liquid crystal molecules,typically either organic or inorganic aligning layers are used, forexample SiO deposited by evaporation is a typical inorganic alignmentlayer. One method to form the alignment layer involves rubbing thesurface by textures or cloths. Polyimides have also been employed forthe surface alignment of layers. Polyimide is coated onto the substratesbearing electrodes by a spinner and then cured to form a layer ofapproximately 50 nm thickness. Then each layer surface is repeatedlyrubbed in substantially one direction with an appropriate material. Ifthe liquid crystal molecules are deposited on this layer they areautomatically aligned in the direction made by the rubbing. It is oftenpreferable if the molecules possess a small angle pre-tilt typically2-3°. Higher pre-tilts are sometimes required.

The two substrates are then fixed together for example by adhesive andare kept separate by spacing materials. This results in uniform andaccurate cell spacing. A typical adhesive is an epoxy resin. Thissealing material is usually then precured. The electrodes may then beprecisely aligned for example to form display pixels. The cell is thencured at, for example 100-150° C. At this point the empty liquid crystalcell is complete.

It is at this point that the cell is filled with the liquid crystalmaterial. The opening size in the sealing area of the liquid crystalcell is rather small therefore the cell can be evacuated, for example ina vacuum chamber, and the liquid crystal material forced into the cellvia gas pressure. More than one hole in the sealing area may be used.The empty cell is put into a vacuum chamber and then the vacuum chamberis pumped down. After the cell has been evacuated the open region of thesealant is dipped into the liquid crystal material and the vacuumchamber is brought back to normal pressure. Liquid crystal material isdrawn into the cell as a result of capillary action, external gases canbe applied to increase the pressure. When the filling process iscomplete the hole or holes in the sealant is/are capped and the cell iscured at a temperature above the liquid crystal material clearing pointto make the liquid crystal molecular alignment stable and harden thecapping material.

Polymer liquid crystal molecules tend to be more viscous than lowmolecular weight liquid crystal materials and are therefore moredifficult to align and more difficult to fill into devices. Only liquidcrystal polymers with low molecular weights can be flow filled into acell, and once a degree of polymerisation greater than around 30 or 40repeat units is reached, most liquid crystal polymers become so viscousthat flow filling cells is extremely difficult. Much slower cooling isneeded in order to try and align liquid crystal polymers and thisusually results in poor uniformity of alignment.

Poorly aligned liquid crystal molecules do not result in the fastswitching high contrast materials and devices that are generallyrequired.

The above techniques are suitable for many liquid crystal materialsincluding those devices which use liquid crystal materials which exhibitand utilise the smectic mesophase e.g. ferroelectrics. Suitablealignment techniques may also be found in GB 2210469 B.

Devices containing ferroelectric liquid crystal mixtures can exhibitfast switching times (faster than 100 ms), Clark and Lagerwall, Appl.Phys. Lett., 36, 89, 1980. They can be bistable which means that theycan be multiplexed at high levels using a line-at-a-time scan technique.Ferroelectric materials continue to receive a large amount ofinvestigative attention due to their application in high resolution flatpanel displays. An important feature of devices containing liquidcrystalline materials is that they should exhibit a fast response time.The response time is dependent on a number of factors, one of thesebeing the spontaneous polarisation, denoted Ps (measured in nC cm⁻²). Byadding a chiral dopant to the liquid crystalline mixture the value of Pscan be increased, thus decreasing the response time of the device.Ferroelectric smectic liquid crystal materials, which can be produced bymixing an achiral host and a chiral dopant, use the ferroelectricproperties of the tilted chiral smectic C, F, G, H, I, J, and K phases.The chiral smectic C phase is denoted S_(C) * with the asterisk denotingchirality. The S_(C) * phase is generally considered to be the mostuseful as it is the fastest switching. It is desirable that the materialshould exhibit a long pitch chiral nematic (denoted N*) and S_(A) phaseat temperatures above the chiral smectic phase in order to assistsurface alignment in a device containing liquid crystalline material.Ferroelectric smectic liquid materials should ideally possess thefollowing characteristics: low viscosity controllable Ps and an S_(C) *phase that persists over a broad temperature range, which should includeambient temperature, and exhibits chemical and photochemical stability.Materials which possess these characteristics offer the prospect of veryfast switching liquid crystal containing devices.

Ferroelectric LCDs by Dijon in Liquid Crystals Applications and Uses,vol. 1 Ed. Bahadur, World Scientific Publishing Co. Pte. Ltd, 1990 pp350-360 and references therein discusses alignment processes for smecticphases for low molar mass materials. The filling of cells is believed tobe possible only in the isotropic or nematic phase due to the viscosityof smectic phases. Generally materials with the following phase sequencegive good alignment: ##STR10## whereas materials with the followingphase sequences are more difficult to align: ##STR11##

Typically, therefore, in order to use a liquid crystal material in thesmectic phase it will involve heating the material to the nematic orisotropic phase and allowing it to cool slowly into an aligned smecticstate. Should this technique be applied to a polymer liquid crystalmaterial then the cooling time is usually very much longer in order toassist the alignment, though very often the alignment is poor.

Another class of materials which may contain liquid crystal propertiesare mesogenic substituted organosilsesquixanes. For example see Europeanpatent application 0446 912 A1 Other references include European patentapplications 0348705, 0367222, 0163495A3 and Makromol. Chem., Macromol.Symp., 50, 215-228, 1991.

One of the other problems associated with liquid crystal devices is thations such as K⁺, Na⁺ and ions formed from the decompositon of liquidcrystal material may be present. The source of these ions may be fromthe glass plates (eg from soda glass) or the alignment layer or from thedyes in coloured filters or from the liquid crystal itself. The presenceof these ions may give rise to numerous problems such as so-calledsticky pixels which gives rise to image retention. Other problemsinclude reverse switching, poor contrast ratios, anodic oxidation, poormultiplexing ability. Attempts to overcome these problems have involvedincorporating small amounts (usually 1 or 2%) of macrocyclic material.These macrocycles complex to the ions and slow down their rate ofdiffusion such that many of the above effects are reduced. However manyof the above problems are still present but only to a lesser degreetherefore many of the deleterious effects are still present.

There is a continued need for new liquid crystal materials whichovercome many of the above problems and which possess the propertiesthat allow them to be used in devices including one or more of the knownelectro-optic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further illustrated with reference to the attacheddrawings in which

FIG. 1 is a synthetic scheme for preparing compounds of the invention;

FIG. 2 illustrates a liquid crystal device;

FIG. 3 illustrates a pyroelectric device;

FIG. 4 illustrates a front view of a reflective spatial light modulatordrawn to different scales, in which the materials of the currentinvention may be incorporated;

FIG. 5 illustrates a sectional view of a reflective spatial lightmodulator drawn to different scales, in which the materials of thecurrent invention may be incorporated; and

FIG. 6 illustrates an electrochemical device in which the materials ofthe current invention may be incorporated.

DESCRIPTION OF THE INVENTION

According to this invention there is provided a material of generalformula I: ##STR12## E=0 indicates a non-cyclic system, E=1 indicates acyclic system;

when E=0 then

G is R₃ SiR₁ R₂ (O)_(k)

R₁, R₂, R₃ are independently selected from C₁₋₁₆ alkyl which may bepartly or fully halogenated, H and formula IA: ##STR13## wherein Y is apropyl group which may be partially halogenated with fluorine orchlorine and Y₁ is independently selected from COO, OCO, O, S, CHOH,CHF, CO, CH₂ ;

Q and Q₁ are independently selected from (CH₂)_(n) wherein one or morenon-adjacent methylenes may be replaced by O and

n=0-20;

Z and Z₁ are independently selected from O, S, single covalent bond,COO, OCO; ##STR14## represents any mesogenic group; and MACROCYCLErepresents any macrocycle;

provided that at least one of R₁, R₂, R₃ is selected from formula IA;

k=0 or 1; g=4 or 6 or 8 or 10 or 12; I=3 or 8 provided that:

if k=1, I=3 and x is selected from 6,8,10,12 then g=x;

if k=0, I=8 and g=4 then x=1;

and further provided that G may have up to g different structures forany single compound;

or when E=0 then x=0, k=1, one of R₁, R₂, R₃ is not present;

g=1-10,000;

whichever of R₁, R₂, R₃ are present are selected from C₁₋₁₆ alkyl whichmay be partly or fully halogenated, H and Formula IA provided that atleast one of whichever of R₁, R₂, R₃ are present are selected fromformula IA;

G may have up to g different structures for any single compound;

provided that on each of the terminal silicons all of R₁, R₂ and R₃ arepresent and may be selected from the same groups as whichever of R₁, R₂,R₃ are present are defined;

when E=1 then x=0, k=1, one of R₁, R₂, R₃ is not present;

g=1-10,000;

whichever of R₁, R₂, R₃ are present are selected from C₁₋₁₆ alkyl whichmay be partly or fully halogenated, H and Formula IA provided that atleast one of whichever of R₁, R₂, R₃ are present are selected fromformula IA;

G may have up to g different structures for any single compound.

The mesogenic group is further defined from general structure II##STR15## A, B, D are independently selected from the following rings:##STR16## the above rings may be substituted with one or more of thefollowing substituents in at least one of the available substitutionpositions: F, Cl, Br, CH₃, CN, OR, R and NCS where R is given by C₁₋₅branched or straight chain alkyl;

provided that the total number of rings present is not greater than 4;

W₁ and W₂ are independently selected from COO, OCO, single bond, CH₂CH₂, CH₂ O, OCH₂, O, S, CH═CH, C═C, N═N.

The macrocycle may be chosen from any of the known types of macrocycle.By the term macrocycle is included any of the known cyclic complexingagents such as crown-ethers, cryptands, cavitands, podands, calixarenesand the like. A comprehensive list of suitable materials is provided inJean-Marie Lehn, Ed. Comprehensive Supramolecular Chemistry, Pergamon,1996, 11 volumes. Other complexing agents which may be suitable includeligands such as EDTA and the like.

18-crown-6 may be particularly useful for complexing K⁺ and 15-crown-5for complexing Na⁺.

In a further aspect of the invention one or more of the groups R₁, R₂,R₃ may possess a polymerisable group, such that the compounds of formulaI may be polymerised to form liquid crystal polymers. Polymerisablegroups include double bonds and triple bonds and epoxides.

The following compounds, by way of example, were synthesised accordingto the present invention.

A synthetic scheme for the production of compounds described by thecurrent invention is illustrated in FIG. 1.

There are various catalysts which may be used in the syntheticprocedure, for example Platinum metals and/or compounds of platinummetals. These include Platinum, Palladium, Rhodium and Iridium andalloys containing such compounds consisting at least of one of theplatinum metals and chemical compounds containing platinum metals andmixtures of them.

Preferred is platinum itself, its chemical derivatives and its alloys,which may be bonded or deposited on a supporting structure. Allcatalysts may be used which have been used for the addition ofunsaturated aliphatic materials to hydrogen atoms bonded to Si atoms.

Examples of such catalysts are metallic and finely dispersed platinum,which can be situated on supports such as silicon dioxide, aluminiumoxide or charcoal. Further examples are derivatives or complexes ofplatinum for example PtCl₄, Na₂ PtCl₄ * 4H₂ O, H₂ PtCl₆ * 6H₂ (Speier'scatalyst), platinum-olefin complexes, platinum-alkanol complexes,platinum-alkanolate complexes, platinum-ether complexes,platinum-aldehyde complexes, platinum-ketone complexes, includingreaction products of H₂ PtCl₆ and cyclohexanone, Platinum-vinylsiloxanecomplexes especially platinumdivinylsiloxane complexes with or withoutthe presence of detectable inorganically bonded halogen,platinum-divinyl tetraethyidisiloxane complex in xylene as disclosed inB. D. Karstedt, U.S. Pat. No. 3.814.730, 1974, available from FluorochemLtd, bis-(gamma-picolin)-platinum dichloride,trimethylene-dipyridine-platinum-dichloride,dicyclopentdieneplatinum-chloride, dimethylsulfoxydiethylenplatinum-(II)-dichloride as well as reaction products of platinumtetrachloride with olefin and primarary amine or secondary amine orprimary amine and secondary amine as well as the reaction product ofplatinum tetrachloride dissolved in 1-octene with sec. butylamine.

The platinum catalyst is used preferentially in amounts of 0.2 to 1000ppm (by weight) (amount of weight per million amounts of weight)calculated as the amount of weight of the elemental platinum relative tothe amount of weight of the reactant side chain given in FIG. 1.

Reaction conditions refer to the coupling of the siloxane core to themesogenic group. The reaction temperature is chosen between the meltingtemperature of the solvent or the solvent mixture and its boilingtemperature, approximately 110° C. in the case of toluene.

For the synthesis of materials with a structure commonly described as acage (D. Hoebbel, W. Wieker, Z. anorg. alig. Chem., 1971, 384, 43; D.Hoebbel, G. Garzo, G. Engelhardt, E. Lippma, M. Alla, Z. anorg. allg.Chem., 1980, P. G. Harrison, R. Kannengiesser, J. Chem. Soc. Chem.Commun. 1996, 415 reviewed in R. H. Baney, M. Itoh, A. Sakakibara, T.Suzuki,Chem Rev. 1995, 95, 1409) reaction temperatures between 4 to 40°C. in toluene as solvent with Karstedt's catalyst as catalyst show fromthe viewpoint of ease of synthesis the best results, if the aim is theavoidance of side reactions of the silicone atoms of the cage.

The reaction can be carried out in the absence or in the presence of asolvent. The term solvent does not mean that the reaction componentshave to be dissolved completely. The reaction can be carried out insuspension or emulsion of one or more of the reaction components. Fromthe viewpoint of the ease of production inert organic solvents show themost desirable performance.

The solvent can be chosen from a common solvent or a mixture of commonsolvents. Examples of solvents are: alkanols e.g. methanol, ethanol,n-propanol, iso-propanol, n.-, sec. and tert. butanol, ester e.g.methylacetate, ethylacetate, n. and iso propylacetate, n. and sec. andtert. butylacetate, ethylformiate, diethylcarbonate, ether e.g.diethylether, tetrahydrofuran, dioxan, di-n-propylether, di-n-butyletherand anisol, cresol, chlorinated hydrocarbons e.g. dichloromethane,trichloromethane, tetrachloromethane, 1,2 dichloromethane,1,1,1-trichloroethane, trichloroethylene, chlorobenzene, hydrocarbonse.g. pentane, n-hexane, cyclohexane, isomer mixtures of hexane, isomermixtures of heptane, octane, isomer mixtures of octane, mixtures ofdifferent alkanes known as petrol ethers, benzene, toluene, xylene ormixtures thereof can be used. Preferentially solvents likedichloromethane, benzene, tetrahydrofuran, diethylether and toluene andmixtures thereof are used.

The coupling reaction between the siloxane core and the mesogenic groupcan be carried out at ambient pressure, this means at approximately 0.1MPa (abs.) or at pressures of 0.01 to 0.5 MPa (abs.).

The reaction can be carried out in the presence of O₂ as outlined by L.N. Lewis et al. J. Am. Chem. Soc., 1990, 112, 5998 or by M. Moran, C. M.Casado, I. Cuadrodo, J. Losada, Organometallics, 1993, 12, 4327; orequally in the absence of O₂.

The final products of the invention may be obtained by the reaction of(G)g(SiO_(1/2))_(x) given in the general formula 1 when at least one ofthe groups of (G)_(g) contains a component Si--H, with a material of thegeneral formula 1A, providing at least one unsaturated aliphatic groupis present. Preferably the unsaturated group is a terminal group and isin the position Y of formula IA.

The liquid crystalline organosilicone compounds of the invention may beprepared by dissolving a material containing at least one SiH group andmaterials containing double bonds and liquid crystalline groups in asolvent together with a platinum catalyst or a solvent mixture.

The materials can be synthesised according to the following procedures.##STR17##

Core A can be obtained by a method outlined in EP 01 63495 oralternatively it is commercially available from Fluorochem Ltd., OldGlossop, Derbyshire, UK. ##STR18## Synthesis ofOctakis(hydrodimethylsiloxy)-octasilsesquioxane, Core B.

Tetramethylammoniumsilicate (4.7 g, 0.05 mol) was added as a 10% aqueoussolution to a solution of heptane (100 ml), dimethylformamide (200 ml)and dimethylchlorosilane (100 ml) which had been previously stirred for20 min. The weakly exothermic reaction was then cooled slowly to 4° C.,and 1l of water, at the temperature of 4° C., was added slowly. Theorganic phase was separated from the aqueous phase and then washed withwater until acid free. The organic solution was concentrated byevaporation under reduced pressure, and resulting mixture was cooled to4° C. in order to facilitate the precipitation ofoctakis(hydrodimethylsiloxy)-octasilsesquioxane as a white solid, whichwas isolated after purification by recrystallisation from acetone; yield1.48 g (73.8%). ν(KBr disc) (cm⁻¹): 2960 (C--H), 2142 (Si--H), δ_(H)(270 MHz, CDCl₃) (ppm): 4.7 (1 H, s, Si--H), 0.2 (6H, s Si--CH₃), δ_(Si)(53.5 MHz, CDCl3) (ppm): 0.5 (H--Si--CH₃), -108.8 (Si-(O)₄ -) ##STR19##Synthesis of Core C Synthesis of the tetraethylammoniumsilicate

113 g tetraethoxysilane was added dropwise to a solution consisting of206 g 40% aqueous solution of tetraethylammoniumhydroxide (FlukaChemicals, Gillingham, UK) and 100 ml water. The reaction mixture wasstirred for 24 h at room temperature. The solvent was removed in vacuoat room temperature and the residue was crystallised at 4° C.

Sylilation

22 g of the tetraethylammoniumsilicate are added slowly to a solutionkept at 4° C. consisting of dimethylformamide (80 ml), heptane (80 ml)and dimethylchlorosilane 80 ml (69.1 g). During the addition thetemperature of the reaction mixture rose to 12° C. Subsequently heptane200 ml was added and the organic phase was washed with water until theaqueous phase was found to be neutral. The organic phase was dried overNa₂ SO₄ filtered and the solvent was removed in vacuo. At 4° C. the slowformation of crystals was found. The first crop yielded after 60 days0.4 g (5% yield). ν(KBr disc) (cm⁻¹): 2960 (C--H), 2142 (Si--H), δ_(H)(270 MHz, CDCl₃) (ppm): 4.8 (1H, s, Si--H), 0.2 (6H, s Si--CH₃), δ_(Si)(53.5 MHz, CDCl₃) (ppm):) 0.5 (H--Si--CH₃), -98.3 (Si-(O)4-).

The spectroscopic and analytical data are in line with the proposedstructure of Hexakis(hydrodimethylsiloxy)-hexasilsesquioxane Core C.##STR20## Synthesis of Core D

Compounds comprising Core D may be purchased from ABCR GmbH & Co KG,Schoemperien str. 5, D7500 Karlsruhe 21. At least one of R₁, R₂, R₃ R₄is H. A particularly suitable example is (50-55) methylhydro-(45-50)dimethylsiloxane wherein the degree of polymerisation is approximately20. ##STR21##

Core E and analogues containing higher amounts of methylhydrosiloxygroups can be obtained from Fluorochem Ltd, Old Glossop, Derbyshire SK139RY or by a synthetic procedure described by Richards et al in J. Chem.Soc. Chem. Commun. 95, 1990.

Synthesis of the Side Chains.

The synthetic methods by which the various sidechains can be obtainedare commonly known in the field of liquid crystals and have beenoutlined in Side Chain Liquid Crystals, Ed. C. B. McArdle, Blackie,London, 1989, Ferroelectric Liquid Crystals, Ed. J. W. Goodby, Gordonand Breach Science Publishers, Philadelphia and in the referencestherein.

The following synthetic pathway is exemplary of the methods used forattaching mesogenic plus macrocyclic groups to siloxane cores and isillustrated in FIG. 1.

4-Methoxycarbonyloxybenzoyl chloride (freshly prepared from4-methoxycarbonyloxybenzoic acid (1) and thionyl chloride) was reactedwith 1,4,7,10-tetraoxa-13-azacyclopentadecane in the presence oftriethylamine to give the protected crown (2). The protecting group wasremoved by dissolving compound 2 in ethanol and adding ammonia solution(0.88 v/v) dropwise and stirring until the reaction was complete.4-(Hex-5-en-1-oxy)biphenyl4'-carboxylic acid (5) was prepared from thereaction of 4-hydroxybiphenyl-4'-carboxylic acid (4) with hexene-6-ol inthe presence of diethylazadicarboxylate and triphenylphosphine followedby flash column chromatography and recrystallisation. The monomer wasobtained by the reaction of the13-[4-hydroxybenzoyl]-1,4,7,10-tetraoxa-13-azacyclopentadecane and4-(hex-5-en-1-oxy)biphenyl-4'-carboxylic acid in the presence ofdicyclohexylcarbodiimide and 4-pyrrolidinopyridine.

Example 1 is a combination of core A and side chain (see FIG. 1).Example 2 is core D and side chain (see FIG. 1).

Synthesis of Example 1

A solution of side chain (see FIG. 1) (0.5 g, 1.03 mmol), 3.0-3.5%solution of Karstedt's catalyst available from Fluorochem Ltd, OldGlossop, Derbyshire, in xylene (3 μl) and toluene (15 ml) was prepared.A gentle stream of air was blown through the solution for 20 seconds. Asolution of core A (tetrakis-(dimethylsiloxy)silane) (0.057 g, 0.17mmol) (available from Fluorochem) in dry toluene was added dropwise atroom temperature over a period of 1 h. During this time the solution,which was originally colourless, developed a faint yellowish colour. Thereaction was monitored by IR spectroscopy. A few minutes aftercompletion of the addition of the monomer no Si--H absorption could bedetected by IR-spectroscopy. A spatula tip of triphenylphosphine wasadded and the solution was concentrated under reduced pressure. Theoligomeric material was purified by column chromatography, usingdichloromethane as solvent and Lipophilic Sephadex LH-20 available fromSigma Chemical Corp., St Louis, Mo. 63178, USA as a stationary phase.After drying in vacuo the product was collected as a white tackysubstance in a yield of 0.26 g (54 per cent). The absence of a peak inthe vicinity of 2.1 ppm in the ¹ H-NMR spectrum shows that no β-additionof the olefins had taken place, and that the oligomeric materials weretherefore single compounds. The spectroscopic and analytic data are inline with the proposed structure of an intact Core A.

Synthesis of Example 2

A solution of side chain (see FIG. 1) (0.47 g, 0.74 mmol), 3.0-3.5%solution of Karstedt's catalyst available from Fluorochem Ltd, OldGlossop, Derbyshire, in xylene (3 μl) and toluene (15 ml) was prepared.A gentle stream of air was blown through the solution for 15 seconds. Asolution of core D (50-55)-methylhydro-(45-50)-dimethylsiloxane (0.074g, 0.65 mmol) (available ABCR GmbH D-7500 Karlsruhe, Germany) in drytoluene was added dropwise at room temperature over a period of 1 h.During this time the solution, which was originally colourless,developed a faint yellowish colour. The reaction was monitored by IRspectroscopy. A few minutes after completion of the addition of themonomer no Si--H absorption could be detected by IR-spectroscopy. Aspatula tip of triphenylphosphine was added and the solution wasconcentrated under reduced pressure. The oligomeric material waspurified by column chromatography, using dichloromethane as solvent andLipophilic Sephadex LH-20 available from Sigma Chemical Corp., St Louis,Mo. 63178, USA as a stationary phase. After drying in vacuo the productwas collected as a white tacky substance in a yield of 0.32 g (58 percent). The absence of a peak in the vicinity of 2.1 ppm in the ¹ H-NMRspectrum shows that no β-addition of the olefins had taken place, andthat the oligomeric materials were therefore single compounds.

    ______________________________________                                        Ex-   silicone                                                                              Tg (° C.)                                                                          Transitions (° C.)                             ample core {ΔCp (J g.sup.-1 K.sup.-1)} {ΔH (J g.sup.-1)}        ______________________________________                                        1     A       -5.4 {0.21} S.sub.1 72.2 {1.80} Iso                               2 D -3.7 {0.19} S.sub.1 62.5 {2.90} S.sub.2 83.1 {0.50} Iso                 ______________________________________                                    

The denominations S₁, S₂ refer to unknown smectic phases.

Some of the compounds described by the current invention may exhibitantiphases. The materials of the present invention may be usefullyemployed in antiferroelectric devices.

An example of the use of a material and device embodying the presentinvention will now be described with reference to FIG. 2.

The liquid crystal device consists of two transparent plates, 1 and 2,for example made from glass. These plates are coated on their internalface with transparent conducting electrodes 3 and 4. An alignment layer5,6 is introduced onto the internal faces of the cell so that a planarorientation of the molecules making up the liquid crystalline materialwill be approximately parallel to the glass plates 1 and 2. This is doneby coating the glass plates 1,2 complete with conducting electrodes sothat the intersections between each column and row form an x, y matrixof addressable elements or pixels. For some types of display thealignment directions are orthogonal. Prior to the construction of thecell the layers 5,6 are rubbed with a roller covered in cloth (forexample made from velvet) in a given direction, the rubbing directionsbeing arranged parallel (same or opposite direction) upon constructionof the cell. A spacer 7 e.g. of polymethyl methacrylate separates theglass plates 1 and 2 to a suitable distance e.g. 2 microns. Liquidcrystal material 8 is introduced between glass plates 1,2 by filling thespace in between them. This may be done by flow filling the cell usingstandard techniques. The spacer 7 is sealed with an adhesive 9 in avacuum using an existing technique. Polarisers 10, 11 may be arranged infront of and behind the cell.

Alignment layers may be introduced onto one or more of the cell walls byone or more of the standard surface treatment techniques such asrubbing, oblique evaporation or as described above by the use of polymeraligning layers.

In alternative embodiments the substrates with the aligning layers onthem are heated and sheared to induce alignment, alternatively thesubstrates with the aligning layers are thermally annealed above theglass transition temperature and below the liquid crystal to isotropicphase transition in combination with an applied field. Furtherembodiments may involve a combination of these aligning techniques. Withsome of these combinations an alignment layer may not be necessary.

The device may operate in a transmissive or reflective mode. In theformer, light passing through the device, e.g. from a tungsten bulb, isselectively transmitted or blocked to form the desired display. In thereflective mode a mirror, or diffuse reflector, (12) is placed behindthe second polariser 11 to reflect ambient light back through the celland two polarisers. By making the mirror partly reflecting the devicemay be operated both in a transmissive and reflective mode.

The alignment layers 5,6 have two functions, one to align contactingliquid crystal molecules in a preferred direction and the other to givea tilt to these molecules--a so called surface tilt--of a few degreestypically around 40° or 5°. The alignment layers 5,6 may be formed byplacing a few drops of the polyimide on to the cell wall and spinningthe wall until a uniform thickness is obtained. The polyimide is thencured by heating to a predetermined temperature for a predetermined timefollowed by unidirectional rubbing with a roller coated with a nyloncloth.

In an alternative embodiment a single polariser and dye material may becombined.

The liquid crystal material 8 when introduced into the cell may consistof liquid crystal material given by formula I which may include liquidcrystal polymers made from compounds of formula I. Should the intentionbe to incorporate liquid crystal polymers in to the cell then thematerial 8 may consist of liquid crystal monomers and a photoinitiator.It may also contain a reagent which will limit the molecular weight ofthe polymer for example a chain transfer reagent and it may also includea thermal initiator.

The monomer material may be aligned before polymerisation using standardtechniques, for example by heating up to and cooling from the isotropicphase or from a liquid crystal phase such as a nematic or chiral nematicphase. It is also possible that the liquid crystal polymer may bealigned by one or more techniques including the use of surface forces,shear alignment or field alignment.

It is possible that following polymerisation there may still be someamount of monomer material remaining. This may be unreacted monomer orlow molar mass additives which do not bear polymerisable groups.

Polymerisation may be carried out by using any of the known techniques.For example the monomer material plus initiator may be exposed to UVlight, heat may also be applied to permit polymerisation within a givenphase of the monomer and/or polymer.

Alternatively the polymerisation process may take place in the presenceof heat and a thermal initiator. However if this technique is used itmay be preferable if it is carried out at a temperature whichcorresponds to a liquid crystal phase of the monomer material.

In-situ polymerisations are described in UK Patent Application GB9420632.3 which also describes the use of chain transfer reagents tocontrol molecular weight of liquid crystal polymers. As mentioned abovethere may also be a chain transfer reagent present in the mixture of thecurrent invention. GB 9514970.4 describes in-situ polymerisations in thepresence of a cationic photoinitiator.

Many of the compounds described by formula I and mixtures includingcompounds of formula I show liquid crystalline behaviour and are thususefully employed in liquid crystal devices. Example of such devicesinclude optical and electro-optical devices, magneto-optical devices anddevices providing responses to stimuli such as temperature changes andtotal or partial pressure changes. The compounds of formula I may alsobe included in a mixture, where the mixture comprises at least twocompounds. Typical mixtures include mixtures consisting of compounds offormula I and also mixtures comprising at least one compound of formulaI and at least one compound not of formula I.

Materials have been proposed for laser addressed applications in whichlaser beams are used to scan across the surface of the material or leavea written impression thereon. For various reasons many of thesematerials have consisted of organic materials which are at leastpartially transparent in the visible region. The technique relies uponlocalised absorption of laser energy which causes localised heating andin turn alters the optical properties of the otherwise transparentmaterial in the region of contact with the laser beam. Thus as the beamtraverses the material, a written impression of its path is left behind.One of the most important of these applications is in laser addressedoptical storage devices, and in laser addressed projection displays inwhich light is directed through a cell containing the material and isprojected onto a screen. Such devices have been described by Khan Appl.Phys. Lett. vol. 22, p111, 1973; and by Harold and Steele in Proceedingsof Euro display 84, pages 29-31, September 1984, Paris, France, in whichthe material in the device was a smectic liquid crystal material.Devices which use a liquid crystal material as the optical storagemedium are an important class of such devices. The use of semiconductorlasers, especially Ga_(x) Al_(1-x) As lasers where x is from 0 to 1, andis preferably 1, has proven popular in the above applications becausethey can provide laser energy at a range of wavelengths in the nearinfra-red which cannot be seen and thus cannot interfere with the visualdisplay, and yet can provide a useful source of well-defined, intenseheat energy. Gallium arsenide lasers provide laser light at wavelengthsof about 850 nm, and are useful for the above applications. Withincreasing Al content (x<1), the laser wavelength may be reduced down toabout 750 nm. The storage density can be increased by using a laser ofshorter wavelength.

The compounds of the present invention may be suitable as opticalstorage media and may be combined with dyes for use in laser addressedsystems, for example in optical recording media.

The smectic and/or nematic properties of the materials described by thecurrent invention may be exploited. For example the materials of thepresent invention may be used in ferroelectric mixtures and devices.

The compounds of the present invention may also be used in pyroelectricdevices for example detectors, steering arrays and vidicon cameras.

FIG. 3 illustrates a simple pyroelectric detector in which the materialsof the present invention may be incorporated.

A pyroelectric detector consists of electrode plates 13,14 at least oneof which may be pixellated. In operation the detector is exposed toradiation R, for example infrared radiation, which is absorbed by theelectrode 13. This results in a rise in temperature which is transmittedto a layer of pyroelectric material 15 by conduction, The change intemperature results in a thermal expansion and a charge is generated.This change in charge is usually small when compared with the chargeoutput due to the change in the spontaneous polarisation, Ps with achange in temperature; this constitutes the primary pyroelectric effect.A change in charge results in a change in potential difference betweenthe electrodes. The charge on each pixel may be read out and theresulting signal is used to modulate scanning circuits in, for example,a video monitor and for a visual image of the infra red scans.

The selective reflective properties of the materials described by thecurrent invention may also allow for materials of the current inventionto be used in inks and paints and they may therefore be useful inanti-counterfeiting operation. They may also be used in so-calledsecurity inks. Other applications include thermal control management,for example the materials may be included in a coating which may beapplied to one or more windows in order to reflect infra-red radiation.

As shown in FIGS. 4 and 5 a spatial light modulator comprises a liquidcrystal cell 16 formed by typically two glass walls 1 and 2 and 0.1-10μm e.g. 2.5 μm thick spacer 7. The inner faces of the walls carry thintransparent indium tin oxide electrodes 3,4 connected to a variablevoltage source 17. On top of the electrodes 3,4 are surface alignmentlayers 5,6 e.g. of rubbed polyimide. Other alignment techniques are alsosuitable e.g. non-rubbing techniques such as evaporation of SiO₂. Alayer 8 of liquid crystal material is contained between the walls 1,2and spacer 7. In front of the cell 16 is a linear polariser 11; behindthe cell 16 is a quarter wave plate 18 (this may be optional) and amirror 19. An example of a linear polariser is a polarising beamsplitter (not illustrated here).

There are a variety of electroclinic devices in which the compounds ofthe present invention may be incorporated. For example in the abovedescription of FIGS. 4 and 5, active back plane driving may be utilised.One of the walls forming the cell may be formed from a silicon substratee.g. a wafer which possesses circuitry for driving pixels.

For many of these devices there exists an optimum thickness for the cellwhich is related to the birefringence (Δn) given by: ##EQU1## whereinλ=wavelength of operation

Δn=birefringence of liquid crystalline material

m=integer.

Some suitable methods for driving electroclinic devices described by thepresent invention may be found in UK patent application GB-2 247 972A.

The mode of operation of the devices described by the current inventionincludes either amplitude modulation or phase modulation. Similarlydevices may be used in reflectance or transmissive mode.

The materials of this aspect of the invention may be used in many of theknown forms of liquid crystal display devices, for example chiralsmectic electro-optic devices. Such a device may comprise a layer ofliquid crystal material contained between two spaced cell walls bearingelectrode structures and surface treated to align liquid crystalmaterial molecules. The liquid crystal mixtures may have manyapplications including in ferroelectric, thermochromic and electroclinicdevices. Further examples of uses for the current materials may be foundin Chem. Rev. 1995, 95, 1409-30.

The compounds of the present invention may be mixed with each other toform useful liquid crystal mixtures, they may also be used with otherliquid crystal polymers or low molar mass non-polymer liquid crystalmaterials.

Suitable devices in which the materials of the current invention may beincorporated include beam steerers, shutters, modulators andpyroelectric and piezoelectric sensors.

The materials of the present invention may also be useful as dopants inferroelectric liquid crystal devices, which may be multiplexed, or theymay be used in active backplane ferroelectric liquid crystal systems.The materials of the present invention may also be useful as hostmaterials. The materials of the present invention may be included inmixtures which also contain one or more dopants.

Compounds of formula I may be mixed with a wide range of hosts, forexample smectic hosts to form a useful liquid crystal composition. Suchcompositions can have a range of Ps values. Compounds of formula I maybe mixed with one or more of the types of hosts VIII-XIII. Thesedifferent types of hosts may be mixed together to which the compound ofgeneral formula I may also be added.

Typical hosts include:

The compounds described in PCT/GB86/00040, e.g. of formula VIII##STR22## where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy.

The fluoro-terphenyls described in EPA 84304894.3 and GBA 8725928, e.g.of formula IX ##STR23## where R₁ and R₂ are independently C₃ -C₁₂ alkylor alkoxy, x is 1 and F may be on any of the available substitutionpositions on the phenyl ring specified.

The difluoro-terphenyis described in GBA 8905422.5, e.g. of formula X##STR24## where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy.

The phenyl-pyrimidines described in WO 86/00087, e.g. of formula XI.##STR25## including those compounds where R₁ is C₃ -C₁₂ alkyl and R₂ isgiven by the general formula (CH₂)_(n) --CHXCH₂ CH₃, where n is 1 to 5and X is CN or Cl.

The compounds described by R Eidenschink et al in Cyclohexanederivativemit Getilteneten Smektischen Phasen at the 16^(th) Freiberg LiquidCrystal Conference, Freiberg, Germany, p8. Available from E Merck Ltd,Germany, e.g. of formula XII. ##STR26## including those compounds whereR₁ and R₂ are independently C_(1-C) ₁₅ alkyl.

The difluoro-phenyl pyrimidines described at the 2^(nd) InternationalSymposium on Ferroelectric Liquid Crystals, Goteborg, Sweden, June 1989by Reiffenrath et al, e.g. of formula XIII ##STR27## including thosecompounds where R₁ and R₂ are independently C₃ -C₉ alkyl.

The materials of the current invention may also be useful inthermochromic devices, for example those devices described by D. G,McDonnell in Thermochromic Liquid Crystals, Critical Reports on AppliedChemistry, vol. 22, edited by G. W. Gray, 1987 pp120-44 and referencestherein.

The materials described by the current invention may be incorporatedinto electrochemical devices. Further, the materials may be processed asthin and flexible films for use in various applications such asthin-film batteries and afford high anisotropic conductivity.

An electrochemical device incorporating materials of the presentinvention is described in FIG. 6. An electrochemical device consists ofan anode 20, typically made from metal and a cathode 21 preferably acomposite cathode (see Scrosati et al in Applications of ElectroactivePolymers, Ed. B. Scrosati, Chapman & Hill, London 1993. Between theanode 20 and cathode 21 is sandwiched an electrolyte 22 which istypically made from a polymer matrix that is doped with one or moreionic compounds (i.e. salts) containing cations which are mobile in anapplied electric field. High conductivity may be obtained by using anappropriately selected concentration of charge carriers achieving a highionic conductivity--see Bruce et al in J. Chem. Soc. Farad. Trans.,(1993), 89, 3187-3203. Conductivity may be promoted by using polarpolymers which show high dielectric constants. The salts which may beused may be chosen from any of the known types including those thatpossess silver or lithium ions, e.g. LiBF₄, LiClO₄, LiSO₃ CF₃, Li(NSO₂CF₃)₂. Thin films of electrolytes may be prepared by pouring a solutionof polymer and salt into a mould and controlling the rate of evaporationof the solvent--see Scrosati et al in Applications of ElectroactivePolymers, Ed. B. Scrosati, Chapman & Hill, London 1993. This techniquemay be varied by spin coating of the polymer/salt solution under aconstant nitrogen stream in a centrifuge on a flat non-tacky substrate.This technique may be used to produce free- standing, macroscopicallyordered liquid-crystalline polymeric films.

Materials described by the current invention may be used as additives indevices such as those described in FIG. 6 in order to improve the ionicconductivity for example see Mehta and Kaeriyama in Makromol. Chem.Phys. 167, 609-619 1996.

What is claimed is:
 1. A material of general formula I: ##STR28## whereE=0 indicates a non-cyclic system, and E=1 indicates a cyclic system;Gis R₃ SiR₁ R₂ (O)_(k) R₁, R₂, R₃ are independently selected from C₁₋₁₆alkyl which may be partly or fully halogenated, H and formula IA:##STR29## wherein Y is a propylene group which may be partiallyhalogenated with fluorine or chlorine and Y₁ is independently selectedfrom COO, OCO, O, S, CHOH, CHF, CO or CH₂ ;Q and Q₁ are independentlyselected from (CH₂)_(n) wherein one or more non-adjacent methylenes maybe replaced by O and n is 0 to 20; Z and Z₁ are independently selectedfrom O, S, a single covalent bond, COO or OCO; ##STR30## representsmesogenic group and is given by the general structure II ##STR31## A, B,D are selected from the following rings: ##STR32## and the above ringsmay be substituted with one or more of the following substituents in atleast one of the available substitution positions: F, Cl, Br, CH₃, CN,OR, R or NCS where R is a C₁₋₅ branched or straight chain alkyl,provided that the total number of rings present is not greater than 4;and W₁ and W₂ are independently COO, OCO, a single bond, CH₂ CH₂, CH₂ O,OCH₂, O, S, CH═CH, C.tbd.C, or N═N, and MACROCYCLE represents anymacrocycle; provided that at least one of R₁, R₂, R₃ is selected fromformula IA; k=0 or 1; g=4 or 6 or 8 or 10 or 12; I=3 or 8 providedthat:if k=1, I=3 and x is selected from 6,8,10,12 then g=x; if k=0,I=8and g=4then x=1; and further provided that G may have up to gdifferent structures for any single compound; or when E=0 then x=0, k=1,one of R₁, R₂, R₃ is not present; g=1 to 10,000; whichever of R₁, R₂, R₃are present are selected from C₁₋₁₆ alkyl which may be partly or fullyhalogenated, H and Formula IA, provided that at least one of whicheverof R₁, R₂, R₃ are present are selected from formula IA; G may have up tog different structures for any single compound; provided that on each ofthe terminal silicons all of R₁, R₂ and R₃ are present and may beselected from the same groups as whichever of R₁, R₂, R₃ are present aredefined; when E=1 then x=0, k=1, one of R₁, R₂, R₃ is not present;g=1-10,000; whichever of R₁, R₂, R₃ are present are selected from C₁₋₁₆alkyl which may be partly or fully halogenated, H and Formula IAprovided that at least one of whichever of R₁, R₂, R₃ are present areselected from formula IA; and G may have up to g different structuresfor any single compound; provided that when aromatic E=0 and the systemis linear and the MACROCYCLE comprises an aromatic moiety then the groupY₁ is attached to a non-aromatic part of the MACROCYCLE.
 2. A materialaccording to claim 1 wherein the macrocycle is selected from thefollowing: ##STR33## wherein the point of attachment from the Y₁ groupto the macrocycle is at any of the available attachment point on themacrocycle.
 3. A material according to claim 2 wherein the macrocycle is##STR34## wherein the point of attachment from the Y₁ group to themacrocycle is at any of the available attachment points on themacrocycle.
 4. A material according to claim 3 wherein the mesogenicgroup is chosen from: ##STR35## and Y₁ is CO, Q₁ is (CH₂)_(n) where n=0and Z₁ =single covalent bond;and Y is propylene, Q is (CH₂)_(n) wheren=0-7 and z=0.
 5. A liquid crystal mixture containing any of thecompounds of claim 1 and a material of the following general formula:##STR36## where R₁ and R₂ are independently C₁ -C₁₂ alkyl or alkoxy; andF₂ means there are 2 fluorines substituted on any of the availablesubstitution positions.
 6. A liquid crystal mixture comprising at leastone of the compounds of claim
 1. 7. A ferroelectric mixture comprisingat least one of the compounds of claim
 1. 8. A cholesteric liquidcrystal mixture comprising at least one of the compounds of claim
 1. 9.A liquid crystal mixture containing any of the compounds of claim 1 anda material of the following general formula: ##STR37## where R₁ and R₂are independently C₃ -C₁₂ alkyl or alkoxy.
 10. A liquid crystal mixturecontaining any of the compounds of claim 1 and a material of thefollowing general formula: ##STR38## where R₁ and R₂ are independentlyC₃ -C₁₂ alkyl or alkoxy, x is 1 and F may be on any of the availablesubstitution positions on the phenyl ring specified.
 11. A liquidcrystal mixture containing any of the compounds of claim 1 and amaterial of the following general formula: ##STR39## where R₁ is C₃ -C₁₂alkyl and R₂ is the general formula (CH₂)_(n) --CHXCH₂ CH₃, where n is 1to 5 and X is CN or Cl.
 12. A liquid crystal mixture containing any ofthe compounds of claim 1 and a material of the following generalformula: ##STR40## where R₁ and R₂ are independently C₁ -C₁₅ alkyl. 13.A liquid crystal mixture containing any of the compounds of claim 1 anda material of the following general formula: ##STR41## including thosecompounds where R₁ and R₂ are independently C₃ -C₉ alkyl.
 14. A devicecomprising two spaced cell walls each bearing electrode structures andtreated on at least one facing surface with an alignment layer, a layerof a liquid crystal material enclosed between the cell walls,characterised in that it incorporates the liquid crystal mixture asclaimed in claim
 6. 15. A pyroelectric device comprising two spacedelectrodes and a layer of a liquid crystal material enclosed between theelectrodes, characterised in that it incorporates the liquid crystalmixture as claimed in claim
 6. 16. A piezoelectric device comprising twospaced electrodes and a layer of a liquid crystal material enclosedbetween the electrodes, characterised in that it incorporates the liquidcrystal mixture as claimed in claim
 6. 17. A liquid crystalelectro-optical display device characterised in that it incorporates amixture as claimed in claim
 6. 18. An optical recording mediumcomprising a recording layer which comprises one or more compounds ofclaim 1 and a dye material.
 19. An electro-chemical device comprising ananode and a cathode between which is an electrolyte, said electrolytecomprising the material of claim 1.